1. Field of the Invention
The present invention relates to antenna apparatus used in an automatic driving system for automobiles and the like. More particularly, the present invention relates to an antenna apparatus using a nonradiative dielectric waveguide using a high frequency band such as the milliwave band.
2. Description of the Related Art
A known antenna apparatus is described with reference to FIG. 14. FIG. 14 is an exploded perspective view of the known antenna apparatus.
Referring to FIG. 14, a known antenna apparatus 110 includes an upper conductor plate 111 and a lower conductor plate 112 made of aluminum, a dielectric strip 113 made of polytetrafluoroethylene, which is held between the upper conductor plate 111 and the lower conductor plate 112, and a cylindrical dielectric resonator 127 disposed at a distance from an end of the dielectric strip 113. A two-slot aperture 114 is formed on the upper conductor plate 111 at a position where the dielectric resonator 127 is disposed.
With this configuration, a nonradiative dielectric waveguide is formed by the upper conductor plate 111, the lower conductor plate 112, and the dielectric strip 113. By adjusting the distance between the upper conductor plate 111 and the lower conductor plate 112 to half a propagating wavelength or less, only the dielectric strip 113 operates as a signal propagation area. An electromagnetic wave input from the outside is propagated through the dielectric strip 113 in a longitudinal-section magnetic (LSM) mode, which in turn is connected with the dielectric resonator 127. The dielectric resonator 127 resonates in an HE111 mode. The electromagnetic wave is radiated from the dielectric resonator 127 via the aperture 114 on the upper conductor plate 111.
Recently, a high frequency band, such as the milliwave band, has been used for automatic driving systems for automobiles. Accordingly, there is an increasing demand for high accuracy in the antenna apparatus, such as by miniaturization of the dielectric resonator. However, the known antenna apparatus includes the dielectric strip and the dielectric resonator disposed at a predetermined separation in accordance with an operating frequency. Disposition of the dielectric resonator in order to satisfy the required characteristics is very difficult.
Polytetrafluoroethylene employed for the dielectric strip has a relatively large coefficient of linear expansion. Variations in temperature cause variations in the distance between the dielectric strip and the dielectric resonator, thus failing to match the operating frequency and increasing return loss. Specifically, the distance between the dielectric strip and the dielectric resonator is small in the milliwave band, so that slight variations in the distance exert a powerful influence on the characteristics of the antenna apparatus.
Accordingly, it is an object of the present invention to provide an antenna apparatus, and an antenna and a transceiver using the same, in which disposition of component parts including a dielectric strip is simple, and characteristics of the antenna apparatus are not susceptible to temperature variations even in a high frequency band, e.g., in the milliwave band.
To this end, according to an aspect of the present invention, there is provided an antenna apparatus including two substantially parallel conductors, a dielectric strip held between the two conductors, an aperture formed on one of the two conductors in the vicinity of the dielectric strip, and a matching section for matching impedance between the dielectric strip and the aperture. The matching section is continuously connected to the dielectric strip in the vicinity of the aperture.
Electromagnetic waves are radiated from the matching section continuously connected to the dielectric strip. There is no need to dispose a dielectric resonator at a distance from the dielectric strip, as in known antenna apparatus. In the antenna apparatus of the present invention, the dielectric strip and the matching section are integrated, eliminating detailed working to dispose the dielectric strip and the dielectric resonator at a predetermined separation. The antenna apparatus of the present invention is stable in characteristics relative to temperature variations.
A stub formed of a dielectric may be continuously connected to the matching section. Thus, reflection characteristics of the antenna apparatus may be improved.
The stub may have a length of xc2xcxcexg where xcexg represents a propagating wavelength. Thus, the reflection characteristics of the antenna apparatus are optimized.
A connecting dielectric strip having a sectional shape differing from that of the dielectric strip may be continuously connected in the vicinity of the matching section. Variations in the shape of the connecting dielectric strip permit variations in an amount of connection between the dielectric strip and the matching section, thereby adjusting the matching between the dielectric strip and the matching section.
The connecting dielectric strip may have a length of xc2xcxcexg relative to the propagating wavelength xcexg. Thus, the amount of connection and the matching between the dielectric strip and the matching section are optimized.
In accordance with another aspect of the present invention, there is provided an antenna including the antenna apparatus and a dielectric lens disposed in the upper part of the aperture of the antenna apparatus.
In accordance with another aspect of the present invention, there is provided a transceiver including the antenna and a transceiver circuit connected to the antenna.
Accordingly, productivity is increased, and the antenna and the transceiver with stable characteristics relative to temperature variations are obtained.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.